1. Field of the Invention
The present invention relates to devices and methods for constructing tubular structural members that allow for variable resistance and stiffness. When the tubular structural member is added to various devices and structures, the tubular structural member gives those devices and structures the ability to change or modify their stiffness or flexing resistance. The tubular structural member is placed over a part of the device along the longitudinal direction over which the stiffness is desired to be changed. The present invention can be used with sports equipment where the user may find it desirable to adjust or change the stiffness of the device, such as hockey sticks, lacrosse sticks, field hockey sticks, bats (for baseball, softball or cricket), golf clubs, fishing rods, skis, snowboards, pole vaulting poles, polo mallets, footwear, masts, scuba fins, bicycles, weightlifting devices, oars and other devices and structures where it may be desirable to change its stiffness. The invention also relates to methods of manufacturing these devices so that the desired stiffness may be set at the time of manufacture.
2. Description of Related Art
application Ser. No. 10/351,307 related to tubular structural members that were inserted into cavities in devices in order to change the stiffness and flexural resistance of that device.
Adjustable sports equipment is known from U.S. Pat. Nos. 6,113,508 and 6,257,997 B1 U.S. that have a cavity in which a stiffening rod is inserted. The use of a stiffening rod, called a structural member, is taught into these references. The cross-section of the structural member can vary along its length with respect to its cross-sectional moment of inertia or plane of flexural resistance. Stiffness then becomes a function of the desired stiffness characteristic of the material or materials at that location and the arrangement of those materials. The present application incorporates disclosure of U.S. Pat. Nos. 6,113,508 and 6,257,997 B1, by reference.
In recent years, sports equipment manufacturers have increasingly turned to different kinds of materials to enhance their sporting equipment. In so doing, entire lines of sports equipment have been developed whose stiffness or flexibility characteristics are but a shade different from each other. Such a shade of difference, however, may be enough to give the individual equipment user an edge over the competition or enhance sports performance.
The user may choose a particular piece of sports equipment having a desired stiffness or flexibility characteristic and, during play, switch to a different piece of sports equipment that is slightly more flexible or stiffer to suit changing playing conditions or to help compensate for weariness or fatigue. Such switching, of course, is subject to availability of different pieces of sports equipment from which to choose.
That is, subtle changes in the stiffness or flexibility characteristics of sports equipment may not be available between different pieces of sports equipment, because the characteristics have been fixed by the manufacturer from the choice of materials, design, etc. Further, the user must have the different pieces of sports equipment nearby during play or they are essentially unavailable to the user.
Golf club shafts may be formed of graphite, wood, titanium, glass fiber or various types of composites or metal alloys. Each varies to some degree with respect to stiffness and flexibility. However, golfers generally carry onto the golf course only a predetermined number of golf club. Varying the stiffness or flexibility of the golf club shaft is not possible, unless the golfer brings another set of clubs of a different construction. Even in that case, however, the selection is still somewhat limited.
U.S. Pat. No. 6,113,508 reveals the use of a stiffening rod in cavities of a golf club shaft to permit the user to adjust the stiffness of the golf club shaft. U.S. Pat. No. 6,257,997 reveals the use of a rotating flexure resistance spine in cavities of a golf club shaft to permit the user to adjust the stiffness of the golf club shaft.